Substantial literature exists with respect to the catalytic hydrogenation of aromatic amines to prepare the corresponding cycloaliphatic amines. Illustrative of this type of reaction is the hydrogenation of methylenedianiline 4,4'-diaminodiphenylmethane, MDA] to the cycloaliphatic amine which is bis(4-aminocyclohexyl)methane, also called PACM, H.sub.12 MDA.
The hydrogenation follows a step-wise reaction sequence, giving first the half hydrogenated cis and trans isomers [p-(4-aminocyclohexylmethyl)aniline, 4-(p-aminobenzyl)aminocyclohexane, H.sub.6 MDA], then reacting further to yield the three bis(4-aminocyclohexyl)methane isomers (cis, cis; cis, trans; and trans, trans) represented by the formulas and reactions as follows: ##STR1##
Some of the early hydrogenation work to produce bis(4-aminocyclohexyl)methanes was done by Whitman and Barkdoll, et al and their work is set forth in a series of U.S. Pat. Nos. 2,511,028; 2,606,924; 2,606,925; and 2,606,928. Basically the processes described in these patents involve the hydrogenation of methylenedianiline at pressures in excess of 200 psig, preferably in excess of 1,000 psig at temperatures within a range of 80.degree. to 275.degree. C. utilizing a ruthenium catalyst for the hydrogenation. The hydrogenation is carried out under liquid phase conditions and an inert organic solvent is used. Most of the references utilize a noble metal such as ruthenium, rhodium, iridium, or mixtures of any of these or with platinum or palladium, either as the hydroxide, oxide, or the metal itself on an inert support. Examples of ruthenium catalysts utilized for the hydrogenation process include ruthenium oxides, such as ruthenium sesquioxide and ruthenium dioxide; ruthenium hydroxide; and ruthenium salts.
U.S. Pat. No. 3,959,374 discloses a process for the preparation of bis(4-aminocyclohexyl)methane by pretreating a mixed methylenedianiline system with a nickel-containing hydrogenation catalyst prior to hydrogenation with ruthenium. The pretreatment was used to overcome low yields (52.4%) and long reaction time associated with nickel and cobalt catalysts. Ruthenium catalysts, although commonly used for hydrogenation, were not suited for hydrogenation of a feed containing impurities. Impurities in the feed caused a rapid decline in activity and hydrogenation efficiency.
In the continued development of processes for manufacturing bis(4-aminocyclohexyl)methanes by hydrogenating methylenedianiline it was found that if the ruthenium was loaded upon a support and the support was alkali-moderated, the catalyst was much more active and catalytically effective in producing the desired hydrogenated bis(4-aminocyclohexyl)methane product. Alkali moderation was effected by contacting the catalyst with an alkali metal hydroxide or alkoxide; also, such alkali moderation of the catalyst could be effected prior to hydrogenation or in situ during the hydrogenation. Representative patents showing the utilization of alkali moderated ruthenium catalysts to hydrogenate methylenedianiline include U.S. Pat. Nos. 3,636,108; 3,644,522; and 3,697,449. Alkali metal and alkaline earth metal nitrates and sulfates have similarly been shown effective in U.S. Pat. No. 4,448,995 under high pressure (4000 psig) hydrogenation conditions. Representative supports disclosed in U.S. Pat. No. 3,697,449 include bauxite, periclase, zirconia, titania, diatomaceous earth, etc.
U.S. Pat. Nos. 3,347,917; 3,711,550; 3,679,746; 3,155,724; 3,766,272 and British Pat. No. 1,122,609 disclose various isomerization and hydrogenation processes to produce bis(4-aminocyclohexyl)methane containing a high trans,trans-isomer content; i.e. an isomer content near equilibrium typically 50% trans,trans, 43% cis,trans and 7% cis,cis. Ruthenium catalysts were used to effect isomerization.
In U.S. Pat. Nos. 4,394,522 and 4,394,523, a process is disclosed for producing bis(4-aminocyclohexyl)methane by carrying out the hydrogenation of methylenedianiline in the presence of unsupported ruthenium dioxide at pressures of at least 2500 psig or in the presence of ruthenium on alumina under pressures of at least 500 psig and preferably from 1500 psig to 4000 psig in the presence of an aliphatic alcohol and ammonia. Other catalysts have been utilized for the hydrogenation of methylenedianiline and examples are shown in U.S. Pat. Nos. 3,591,635 and 3,856,862 which disclose the use of a rhodium component as a catalytic material and each require the use of an alcohol as a solvent. The rhodium is alkali moderated using ammonium hydroxide as a pretreatment or by carrying out the reaction in the presence of ammonia.
The isomeric cycloaliphatic diamines are useful in the preparation of the corresponding aliphatic diisocyanates suitable for forming light stable urethane coatings and lacquers. In earlier experiments involving the hydrogenation of aniline, it was shown that addition of ammonia not only suppresses by-product formation mainly from hydrogenolysis and condensation reactions, but also poisons the catalyst. However, addition of lithium hydroxide and sometimes sodium hydroxide suppresses the hydrogenolysis without the detrimental poisoning of the catalyst. A similar phenomenon has been reported with the hydrogenation of methylenedianiline using lithium hydroxide, and to a lesser extent, with other alkali or alkaline earth hydroxides or alkoxides. Common by-products formed during the hydrogenation of methylenedianiline include the hydrogenolysis products 4-aminodicyclohexylmethane and 4-aminocyclohexylcyclohexenylmethane, the hydrolysis product 4-amino-4'-hydroxydicyclohexylmethane, and higher boilers, mainly, but not exclusively, higher molecular weight secondary amine condensation products. All of these products exist as a number of isomers.
U.S. Pat. No. 4,448,995 teaches that this hydrogenation reaction should be maintained in an anhydrous state or at least maintained so that water concentration is less than 0.5% by weight because failure to do so results in an increase in both the amount of alcohol by-products and higher molecular weight condensation products. In addition, the patent states that alkali nitrates and sulfates, especially those of lithium reduce by-products.
In some comparisons, the presence of lithium hydroxide has been shown to actually result in an increase in the production of higher molecular weight products. (See U.S. Pat. No. 4,946,998.)
The use of platinum group metals to catalyze hydrogenation reactions is known in the art. Because of the high cost of these catalysts, any method for increasing the activity and/or life of the catalysts is desirable and valuable. The use of lithium hydroxide and related materials for such a purpose has been described above. The search for other promoters (also called activators and moderators) is one method for achieving this goal.
Substances that cause a deactivation of the catalyst are called poisons or inhibitors. The only difference between the two is the amount of loss of catalyst activity. For the purpose of this application, the term catalyst poison will be used in referring to all such phenomena. It has been found, generally, that heavy metals either are detrimental (catalyst poisons) or have no effect on platinum group metal catalysts used in hydrogenation reactions. Specifically, it has been found that Pb, Cu, Ni, Bi, and Cr behave as poisons for Pt in the hydrogenation of nitrobenzene in the preparation of aniline. Ag has been found to poison Pd catalysts in the same reaction. A careful study of the ring hydrogenation of rosin derivatives (not containing an amine) showed that the following metals, introduced as nitrates, functioned as catalyst poisons: Pb, Hg, Zn, Cu, Al, Mn, Ti, Mg, Na, Cr, Ni, and Ca. [J. B. Montgomery, et al., Ind. Eng. Chem., 50, 313 (1958)]. Acetates of the following metals have been disclosed as catalyst poisons: Cu, Ag, Au, Zn, Cd, Hg, Tl, In, Ti, Sn, Pb, Bi, Mn, Fe, Co, and Ni. [E. B. Maxted and A. Marsden, J. Chem. Soc. 469 (1940)].
The poisoning of catalysts is essentially a preferential adsorption effect dependent on the attraction between a catalyst and certain types of adsorbed species which are usually, but not always, foreign to the reacting system to be catalyzed. In most cases, the strong adsorptive bond by means of which the poison is held to the catalyst appears to be of a highly specific and chemical nature, the formation of such bonds being apparently dependent on definite types of electronic configuration both in the catalyst and in the poison. Substances are in practice only regarded as poisons if they exert an appreciable inhibitive effect on the catalysis even when present in very small concentrations. This concept of poisoning does not include the mechanical covering of a catalyst surface by less specifically held coatings, such as the cloaking of a catalyst by a layer of gums or waxes or deposit of carbon in organic reactions at high temperature.
The counter-ion of the metal salt can be chosen from a variety of possibilities. However, many are known to cause poisoning. Species with non-bonded electron pairs are known to be deleterious to catalysts. They become strongly attracted to noble metals and catalyst deactivation results. Monatomic ions that possess non-bonded electrons often, but not always act as catalyst poisons. Ions of this type such as halides are occasionally used as counter-ions, but are not preferable. Many sulfur and phosphorus compounds and their analogs with non-bonded electrons on the sulfur and the phosphorus are among the strongest catalyst poisons. Moieties such as sulfates, phosphates, and their analogs which have no non-bonded electrons around the central atom exhibit no catalyst poisoning. Examples of catalyst poisons and non-poisons are shown below: ##STR2## [E. B. Maxted and R. W. D. Morrish, J. Chem. Soc. 252 (1940); 132 (1941)].
Some reduction reactions have induction periods, i.e. a time required before the maximum rate is obtained or before hydrogenation occurs. Ruthenium catalysts are known to be particularly inclined to exhibit induction periods, but this phenomenon has also been observed with other noble metals. In the reduction of aldehydes to alcohols, stannous chloride was shown to be an effective promoter in eliminating the induction period and giving a slight increase in rate. [P. N. Rylander and J. Kaplan, Engelhard Ind. Tech. Bull., 2, 48 (1961); P. N. Rylander, et al., Engelhard Ind. Tech. Bull., 8, 99 (1967).]
In contrast the process of the present invention has found that when a transition and/or lanthanide metal salt is used as a promoter in a catalytic hydrogenation reaction of aromatic amines, there is an increase in the reaction rate, decrease or elimination of the induction period, and a decrease in the amount of the high boiler by-products of the reaction.